Getting associated texture with an exported wavefront object
The OBJ consists of two parts:


.obj file with the geometry etc.
.mtl the material library with the associated textures


when you export from blender, make sure you check the "write materials" checkbox. (then you get the .mtl file)

The other thing that is relatively annoying with blender is that it exports absolute paths to the textures. Some applications expect a relative path though. You can open your mtl file in a text editor (e.g. Sublime Text) and change the paths manually. 

hope that helps.

edit: the obj format is relatively easy (so is the mtl) you can basically write/ manipulate your materials in the text editor (add/remove textures, change or add values)